Hydrophilic nonwoven fabric

ABSTRACT

The present invention is to provide a hydrophilic nonwoven fabric which can reveal hydrophilicity even after exposure to high temperature. The hydrophilic nonwoven fabric comprising an olefinic polymer containing a hydrophilic agent is characterized in that hydrophilicity can be revealed after heating treatment for an hour at 60° C. The nonwoven fabric is manufactured by using an olefinic polymer (B) and a master batch where a hydrophilic agent is included in an olefinic polymer (A), wherein an MFR (melt flow rate) of a master batch is preferably the same as or lower than the MFR of an olefinic polymer composition forming the nonwoven fabric.

TECHNICAL FIELD

The present invention relates to a hydrophilic nonwoven fabric. More specifically, the invention relates to a hydrophilic nonwoven fabric which can maintain hydrophilicity even when the hydrophilic nonwoven fabric is exposed to the environment of high temperature.

BACKGROUND ART

A method of coating a fiber with a hydrophilic agent and a method of adding a hydrophilic agent to a resin forming fibers have been known for a conventional method of allowing hydrophilicity to nonwoven fabrics (for example, refer to JP2003-201670A). Also, a hydrophilic agent compounded to a resin was disclosed in WO2002-42530A. However, when a method of allowing hydrophilicity by coating was repeatedly used, it was difficult to maintain hydrophilic ability continuously because a coating agent was fallen off. Also, a method of adding a hydrophilic agent to a resin had hydrophilicity continuously, but it was difficult to maintain hydrophilic ability after exposure to high temperature.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a hydrophilic nonwoven fabric which can reveal hydrophilicity even after exposure to high temperature.

The present inventor has found hydrophilic nonwoven fabrics which have hydrophilicity continuously and maintain heat resistant hydrophilicity by adding a specific master batch containing a hydrophilic agent to a resin. Thus, the present invention has been completed.

Namely, the present invention provides a nonwoven fabric comprising polyolefin in which liquid transport is recognized within 10 seconds as measured by the liquid transport speed specified in EDANA 150 2-93 (or the more recent version EDANA 150 4-99) after heating treatment for an hour at 60° C. The content of EDANA 150 2-93 (EDANA 150 4-99) is hereby incorporated by reference.

Polyolefin to be used for the present invention is an olefin polymer containing a hydrophilic compound. Also, one of desirable embodiments of the present invention is a nonwoven fabric, wherein polyolefin to be used for the present invention is an olefin polymer where a hydrophilic compound is contained as one mixture compounded.

According to an appropriate embodiment of the present invention, the nonwoven fabric is manufactured by using an olefinic polymer (B) and a master batch where a hydrophilic agent is included in an olefinic polymer (A), wherein an MFR (melt flow rate) of the master batch is the same as or lower than the MFR of an olefinic polymer composition forming the nonwoven fabric.

The present invention provides a method for manufacturing a hydrophilic nonwoven fabric, wherein the hydrophilic nonwoven fabric is manufactured by extruding from a spinning nozzle after melting and compounding (kneading) a master batch where a hydrophilic agent is included in an olefinic polymer (A) together with an olefinic polymer (B) at an extruder, wherein the MFR of the master batch is the same as or lower than the MFR of an olefinic polymer composition forming the nonwoven fabric.

Effect of the Invention

According to the present invention, it is possible to provide a hydrophilic nonwoven fabric which can reveal hydrophilicity even when the nonwoven fabric is exposed to an environment of high temperature and is superior in heat resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

An olefinic polymer, a hydrophilic agent, a nonwoven fabric and a composite nonwoven fabric in which the nonwoven fabrics are laminated according to the present invention will be described in more detail below.

In the present specification, a nonwoven fabric is sometimes described as a “hydrophilic nonwoven fabric”, in which liquid transport is recognized within 10 seconds as measured by the liquid transport speed specified in EDANA 150 2-93. Also, a nonwoven fabric comprising polyolefin is sometimes described as a “polyolefin nonwoven fabric”.

As an olefinic polymer (B) which can be used for the nonwoven fabric of the present invention, there can be mentioned, for example, ethylene-based polymers such as a homopolymer of ethylene, a copolymer of ethylene and other α-olefin and the like; propylene-based polymers such as a homopolymer of propylene, a copolymer of propylene and other α-olefin and the like; or a mixture thereof. Of these polymers, a propylene-based polymer is preferred.

[Propylene-based Polymer]

A propylene-based polymer which can be used for the present invention includes a homopolymer of propylene or a copolymer of propylene as a main monomer component and at least one other α-olefin. As other α-olefins, there can be mentioned, for example, α-olefins having 2 to 20 carbon atoms and preferably having 2 to 8 carbon atoms such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like. These homopolymers or copolymers can be used singly (one kind) or in combination of 2 or more kinds.

As for a propylene-based polymer which can be used for the present invention, the MFR is usually 15 to 2000 g/10 min., preferably 1.5 to 900 g/10 min., more preferably 10 to 100 g/10 min., and further preferably 30 to 80 g/10 min. The MFR is measured on the basis of the standards according to each resin. For example, a propylene-based polymer is measured under a load of 2.16 kg at 230° C. in accordance with ASTM D1238.

Mw/Mn, that is, the ratio of weight average molecular weight (Mw) and number average molecular weight (Mn) of a propylene-based polymer which can be used for the present invention is usually 1.5 to 8 and preferably 1.5 to 5. Furthermore, Mw/Mn of 1.5 to 3 is preferred from the facts that spinnability is good and fibers having particularly excellent fiber strength can be obtained. In the present invention, good spinnability means that no thread breakage occurs during drawing and extending from the spinning nozzle, and fusion of filaments does not occur. In the present invention, Mw/Mn is measured by GPC (gel permeation chromatography) in a usual method.

Other components may be added to the resin to be used for production of the nonwoven fabric of the present invention as desired, within the range of not damaging the object of the present invention. Other components include additives that are combined to provide further functions, which can be appropriately combined with by the proper selection for each use.

As other components, there can be mentioned, for example, known heat resistant stabilizers, weather resistant stabilizers, various stabilizers, anti-static agents, slipping agents, anti-blocking agents, anti-fogging agents, lubricants, dyes, pigments, natural oil, synthetic oil, waxes, fillers and the like.

As stabilizers, there can be mentioned, for example, anti-aging agents such as 2,6-di-t-butyl-4-methylphenol (BHT) and the like; phenol-based antioxidants such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydoxyphenyl)propionate]methane, β-(3,5-di-t-butyl-4-hydroxyphenyl)propionic acid alkyl esters, 2,2′-oxamidobis[ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)]propionate, Irganox 1010 (trademark of hindered phenol type antioxidant) and the like; fatty acid metal salts such as zinc stearate, calcium stearate, calcium 1,2-hydroxystearate and the like; polyhydric alcohol fatty acid esters such as glycerine monosterate, glycerine distearate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate and the like. These stabilizers can also be used in combination.

Furthermore, as fillers, there can be mentioned, for example, silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, pumice powders, pumice balloon, aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, dolomite, calcium sulfate, potassium titanate, barium sulfate, calcium sulfite, talc, clay, mica, asbestos, calcium silicate, montmorillonite, bentonite, graphite, aluminum powders, molybdenum sulfide and the like.

[Hydrophilic Agent]

A hydrophilic agent to be used for the present invention is not particularly restricted as far as the hydrophilic agent can be made to a master batch. Specifically, the hydrophilic agents include nonionic surfactants such as fatty acid glyceride, alkoxylated alkyl phenol, polyoxy alkylene fatty acid ester, alkyl polyoxy ethylene alcohol, fatty acid amide and the like; a group of surfactants such as fatty acid salts, alkyl sulfuric acid ester salts, alkyl benzene sulfonic acid salts, alkyl naphthalene sulfonic acid salts, dialkyl sulfosuccinic acid salts, special anion and the like; those properly selected from a compound group such as polyethylene glycol, a copolymer of vinyl alcohol and ethylene, and a polyether block amide copolymer. These can be used singly or in combination.

Of these agents, those represented by the following formula are preferred. R¹—(hydrophilic oligomer)

-   -   wherein R¹ is a straight-chained or branched alkyl group and         preferably has 22 to 40 carbon atoms. Also, hydrophilic         oligomers are preferably those comprising single or oligomer         unit derived from ethylene oxide, propylene oxide, ethylene         glycol, epichlorohydrin, acrylic acid, methacrylic acid,         ethylene imine, caprolactone, vinyl alcohol and vinyl acetate         and units thereof are made up of 2 to 10.

More preferably, those having the following formula can be mentioned. R¹(OCH₂CH₂)_(x)OH

-   -   wherein x is a number of 2 to 10.

Furthermore, for example, CH₃CH₂(CH₂CH₂)₁₃CH₂CH₂(OCH₂CH₂)_(2.5)OH can be specifically mentioned. Herein, the adduct number 2.5 of ethylene oxide is an average value.

These compounds of the structure can be used in combination of 2 or more kinds.

A hydrophilic agent which can be applied to the present invention, for example, when the olefinic polymer (A) is a propylene-based polymer, is preferably included to the olefinic polymer (A) in the form of a master batch at a ratio of 5 to 70 weight %, wherein the MFR of the olefinic polymer (A) measured under a load of 2.16 kg at 230° C. is 1.5 to 2000 g/10 min. and more preferably 5 to 800 g/10 min. The olefinic polymer (A) to be used here is preferably the same kind as the olefinic polymer (B) forming the nonwoven fabric. Furthermore, the MFR of the master batch to be added is preferably the same as or lower than the MFR of the olefinic polymer composition forming the produced nonwoven fabric. For this reason, the MFR of the propylene-based polymer to which the master batch is added may be equivalent to or lower than the MFR of the master batch.

The range of amount of the master batch is preferably 0.1 to 10 weight % and more preferably 0.5 to 5 weight %. Here, the MFR is the same, which means that the MFR of the olefinic polymer composition and the MFR of the master batch of a hydrophilic agent are viewed the same in consideration of the range of measurement error.

[Nonwoven Fabric]

The intended amount of the hydrophilic nonwoven fabric of the present invention is usually 3 to 100 g/m² and preferably 20 to 60 g/m².

The nonwoven fabric of the present invention is preferably a spunbonded nonwoven fabric or a meltblown nonwoven fabric. The spunbonded nonwoven fabric is produced, for example, by the following method. A hydrophilic agent is added to the olefinic polymer (A) so as to be a predetermined density, and then the mixture is melted and compounded to produce a master batch of a hydrophilic agent (the olefinic polymer (A) used here is preferably the same kind as the olefinic polymer (B) forming the nonwoven fabric). The thus-produced master batch is mixed with the olefinic polymer (B) forming the nonwoven fabric at a predetermined rate, and then the mixture is melted by using an extruder and the like. The melted product is drew from a spinning cap having a spinning nozzle, thus spinning long-fibers. So, the thus-spun composite long-fiber is cooled by cooling fluid and further stress is added to long-fibers by extending air to have a predetermined fiber titer. The long-fiber is collected as it is on the web-forming belt and piled up at a predetermined thickness. Next, entangling treatment using means such as a needle punch, water jet, ultrasonic seal and the like or thermo melting treatment using a heat embossing roll is performed. In case of thermo melting treatment by a heat embossing roll, embossing area of the embossing roll is usually 5 to 30%. Such areas are preferred.

The meltblown nonwoven fabric is produced in the same manner as the spunbonded nonwoven fabric. That is, a hydrophilic agent is added to the olefinic polymer (A) so as to be a predetermined density, and then the mixture is melted and compounded to produce a master batch of a hydrophilic agent. The thus-produced master batch is mixed with the olefinic polymer (B) forming the nonwoven fabric at a predetermined rate, and then the mixture is melted by using an extruder and the like. The melted product is drew from a meltblown spinning cap to obtain fibers. The thus-obtained fibers become traction fine to ultrafine fibers by high-temperature and high-speed gas, and then they are taken for an ultrafine fiber web by a collection device for further performing thermo melting treatment as needed.

The hydrophilic nonwoven fabric of the present invention has excellent heat resistant hydrophilicity. Herein, excellent heat resistant hydrophilicity means that, for example, in a spunbond process, hydrophilic ability is maintained even after heating treatment such as heat embossing process and the like was performed. Especially, the hydrophilic nonwoven fabric of the present invention has a remarkable heat resistant hydrophilicity which can reveal hydrophilicity even after heating treatment for an hour at 60° C. Incidentally, a drying method or a heating method is not particularly restricted thereto.

The nonwoven fabric comprises polyolelfin of the present invention, wherein the hydrophilic agent as described above is contained in polyolefin as one mixture compounded. Whether the hydrophilic agent is compounded or not can be confirmed by treating the nonwoven fabric with water. Namely, when the surface tension of water before treating the nonwoven fabric (for example, dipping and stirring the nonwoven fabric) is compared with the surface tension after treating the nonwoven fabric, if it is reduced, it can be considered that a hydrophilic agent is coated on the fiber forming the nonwoven fabric or dissolution occurs at an intense state even if it is compounded. Usually, the pure surface tension is about 70 to 72 mN/m. However, when an additive or the like is present on the fiber, the pure surface tension also depends on a structure of the additive present on the fiber, but the water surface tension is reduced down to 60 mN/m or less and further down to 55 mN/m or less. The nonwoven fabric of the present invention that is treated with the water is transported within 10 seconds even when the liquid transport speed specified in EDANA 150 2-93 is measured even after treating at room temperature and 60° C. for an hour.

According to the test method of EDANA 150 2-93 (EDANA 150 4-99), the following testing conditions material, reagents, apparatus and procedure are used:

Testing Conditions

Condition the samples of nonwoven and the filter papers to be used as the standard absorbent pad for 24 hours and test at 20° C. and 65% relative humidity; test conditions are to be mentioned in the report (see ERT 60 for tolerances and choice of conditions). ISO 9073-8: 1995 Textiles—Test method for nonwovens—Determination of liquid strike-through time (stimulated urine). (EN 29073 part 8) (For testing conditions specified in ISO 9073-8, refer to ERT 60.)

Material and Reagents

1. Reference absorbent pad, consisting of five layers of reference filter paper (100 mm×100 mm) with the smooth side uppermost and having a mean strike-through time, in 10 determinations without the nonwoven, of (3±0.5) s. [Reference filter paper: ERT FF3 filter paper supplied by Hollingsworth & Vose Company Ltd.]

2. Simulated urine, consisting of a 9 g/l solution of sodium chloride in distilled water with a surface tension of (70±2) mN/m. This surface tension should be checked before each series of tests, as surface can alter tension during storage.

Apparatus

1. Burette, of 50 ml capacity, with a supporting stand.

2. Funnel, fitted with a magnetic valve, giving a rate of discharge of 25 ml in (3.5±0.25) s.

3. Ring stand, to support the funnel.

4. Strike-through plate constructed of 25 mm thick transparent acrylic sheet, of total mass (500±5) g, fitted with corrosion-resistant electrodes consisting of 1.6 mm diameter platinum or stainless steel wire set in grooves of cross-section 4.0 mm×7.0 mm cut in the base of the plate and fixed with quick-setting epoxy resin.

5. Baseplate, of transparent acrylic sheet, approximately 125 mm×125 mm square and 5 mm thick.

6. Electronic timer, which can be read to the nearest 0.01 s.

Procedure

1. Set up the ring stand holding the funnel and position the burette with the tip inside the funnel.

2. Cut the required number of pieces of nonwoven, 125 mm×125 mm, test pieces being selected in accordance with ERT 130.

3. Place one nonwoven test piece on top of one set of 5 reference filter papers on the baseplate. Place the nonwoven on the filter paper in such a way that the side of the nonwoven which is intended to be in contact with the user's skin is uppermost. Ensure that the electrodes in the strike-through plate are clean. Place the strike-through plate on top of the nonwoven with the center of the plate over the center of the test piece. Center the burette and the funnel over the plate.

4. Adjust the height of the funnel so that it is (5±0.5) mm above the top of the cavity in the plate (i.e., 30 mm above the test piece).

5. Ensure the electrodes are connected to the timer. Activate the timer and set the clock to zero.

6. Fill the burette with simulated urine. Keep the discharge valve of the funnel closed and run 5.0 ml of liquid from the burette into the funnel.

7. Open the magnetic discharge valve of the funnel to discharge 5.0 ml of liquid. The initial flow of liquid will complete the electrical circuit and start the timer. It will stop when the liquid has penetrated into the nonwoven and fallen below the level of the electrodes in the strike-through plate.

8. Record the time indicated on the electronic timer.

9. Repeat for the required number of test pieces. (A minimum of 10 tests on test pieces from each sample is recommended.)

The liquid transport speed was measured with a Lister device (available from Lenzing Instruments).

EXAMPLE

Alkyl polyoxy ethylene alcohol (CH₃CH₂(CH₂CH₂)₁₃CH₂CH₂(OCH₂CH₂)_(2.5)OH) was added to a polypropylene resin (S119, MFR=60 g/10 min., manufactured by Mitsui Chemicals, Inc.) as a hydrophilic agent so as to be 60 weight % for melting and kneading, thus producing a pellet of a master batch. The MFR of the master batch was 30 g/10 min. Next, the master batch was added thereto at a ratio of 3 weight parts to 100 weight parts of the polypropylene resin (S119, MFR=60 g/10 min., manufactured by Mitsui Chemicals, Inc.). The resulting mixture was melted at an extruder and draw according to the spunbonding process for embossing processing, thus producing a spunbonded nonwoven fabric having 2.2 denier of fiber titer, 20 g/m² (MFR of the resin composition forming the nonwoven fabric was 60 g/10 min.). Heating treatment of the nonwoven fabric was performed for an hour at 60° C. and left at room temperature. As the result, hydrophilicity was revealed after 2 hours.

In addition, the heating treatment was conducted by hanging a piece of the nonwoven fabric (200 mm×250 mm) in the center of a drier TABAI SAFETY OVEN STS222 manufactured by Espec Corp., operation condition: wind level 5 and temperature 60° C., so that the piece receives dry wind vertically.

Here, in case liquid transport was recognized within 10 seconds for the nonwoven fabric as measured by the liquid transport speed specified in EDANA 150 2-93, the nonwoven fabric was evaluated that it had hydrophilicity.

Comparative Example

Alkyl polyoxy ethylene alcohol (CH₃CH₂(CH₂CH₂)₁₃CH₂CH₂(OCH₂CH₂)_(2.5)OH) was added to a polypropylene resin (HF461X, manufactured by Basell Inc.) as a hydrophilic agent so as to be 60 weight % for melting and compounding, thus producing a pellet of a master batch. The MFR of the master batch was 400 g/10 min. Next, the master batch was added thereto at a ratio of 3 weight parts to 100 weight parts of the polypropylene resin (S119, MFR=60 g/10 min., manufactured by Mitsui Chemicals, Inc.). The resulting mixture was melted at an extruder and draw according to the spunbonding process for embossing processing, thus producing a spunbonded nonwoven fabric having 2.2 denier of fiber titer, 20 g/m² (MFR of the resin composition forming the nonwoven fabric was 60 g/10 min.). Heating treatment of the nonwoven fabric was performed for an hour at 60° C. and left at room temperature. As the result, no hydrophilicity was revealed even after 2 weeks have passed.

INDUSTRIAL APPLICABILITY

Conventionally, in case of heat embossing processing, as hydrophilic ability becomes devitalized due to thermal history thereof, use of goods such as disposable diapers and the like has been restricted. However, the hydrophilic nonwoven fabric of the present invention, which has excellent heat resistant hydrophilicity, can be properly used for medical purposes, sanitary purposes, packaging materials, industrial materials and the like according to the present invention. Specifically, the nonwoven fabric of the present invention can be applied to sheets, pet sheets, soup absorbing sheets such as vegetable, drip sheets, gowns, steamed hand towels, pap materials, labor cloths, wipers, wet tissues, gauzes, dish cloths, towels, hip wipers, toilet cleaners, flooring cleaners, range cleaners, make up removers, glass cleaning and the like. In particular, the nonwoven fabric can be preferably used as members of disposable diapers and sanitary napkins. 

1. A nonwoven fabric comprising polyolefin in which liquid transport is recognized within 10 seconds as measured by the liquid transport speed specified in EDANA 150 2-93 after heating treatment for an hour at 60° C.
 2. The nonwoven fabric according to claim 1, wherein said polyolefin is an olefin polymer containing a hydrophilic compound.
 3. The nonwoven fabric according to claim 1, wherein said polyolefin is an olefin polymer where a hydrophilic compound is contained as one mixture compounded.
 4. The nonwoven fabric according to claim 1, wherein the nonwoven fabric is made from polyolefin formed by using a hydrophilic compound as a master batch where the melt flow index of the master batch is same or lower than the melt flow index of polyolefin.
 5. The nonwoven fabric according to claim 1, wherein the nonwoven fabric is a spunbonded nonwoven fabric or a meltblown nonwoven fabric. 